Plain English Meaning

The setting on the fuel selector that stops fuel from reaching the engine. With it in this position, the engine cannot run because no fuel can get through.

Full Definition

A position on the fuel selector valve that shuts off fuel flow from all tanks to the engine. Selecting OFF isolates the fuel system from the engine and is used during certain emergencies (such as an engine fire) or when securing the aircraft.

Context Anchor

Seen on fuel selectors, fuel shutoff valves, and checklist items for engine start, shutdown, emergency procedures, and securing the airplane.

Derivation

Off comes from Old English words meaning away or away from. That helps here because OFF means the fuel is taken away from the engine by closing the path it would normally flow through.